Isocyanate-terminated polyurethane prepolymers can be modified to improve or add to their basic properties by end-capping the isocyanate groups of the prepolymers with organosilanes. One method described in U.S. Pat. No. 3,632,557 utilizes trihydrocarbyloxysilanes to end-cap the polyurethane prepolymers. The trihydrocarbyloxysilyl-terminated polymers produced by this method, upon curing, form elastomers that are useful in applications that require elastomers with a high modulus of elasticity and high tensile strength, e.g. in sealants used to secure windshields in automobiles.
However, elastomers produced from polyurethane polymers end-capped with trihydrocarbyloxysilanes frequently exhibit insufficient elongation and flexibility to be useful in applications requiring elastomers that are capable of considerable stretching and contracting. For example, the elastomers used in moisture barrier sealants in expansion joints of high rise buildings frequently need the ability to stretch and compress without tearing and cracking. These joints often have widths of six inches or more and changes in temperature can cause expansions and contractions of these joints of .+-.50%. These elastomers formed from polyurethane polymers end-capped with trihydrocarbyloxysilanes in many cases would not be effective as sealants in expansion joints because this application often requires elastomers with higher elongation and more flexibility than is provided by such silanes. Improved elongation and flexibility would also be desirable in elastomers utilized in other applications, e.g., in coatings, gaskets, fiber sizes, adhesives and the like.
Accordingly, it is an object of the present invention to provide improved hydrocarbyloxysilyl-terminated polyurethane polymers and sealant compositions containing such polymers, which upon curing, form elastomeric polymers with improved elongation, improved flexibility and a lower modulus of elasticity.